Warm episode (El Niņo)
conditions rapidly dissipated in the tropical Pacific during March and April
2003, as sea-surface temperature anomalies continued to decrease across the
central and eastern equatorial Pacific and drier-than-average conditions
developed over the central equatorial Pacific (Fig. 1). Significant deceases
in SST anomalies occurred in all of the Niņo
regions during April and early May (Fig. 2 and Fig.
3). By mid-May equatorial
SSTs were near or below normal between 165°W
and the South American coast, with only a small area of residual positive
SST anomalies west of the date line between 155°E
and 175°E (Fig. 3, bottom panel).

Consistent with the cooling trend in SSTs, the equatorial easterlies have
been stronger than average over the central and west-central equatorial
Pacific since late February, and the equatorial SOI has switched from
negative to positive (Fig. 4). In addition, in recent months the depth of
the oceanic thermocline has steadily decreased across the central and
eastern equatorial Pacific, and negative subsurface temperature departures
have developed and intensified in the upper ocean of this region (Fig.
5).
By late-April subsurface temperatures at thermocline depth were below
average throughout the eastern Pacific, with negative anomalies ranging
between -1°C and
-3°C (Fig. 5,
bottom panel). These observed trends in oceanic and atmospheric variables
indicate that a transition to La Niņa
is underway and that La Nina conditions are likely to develop over the next
few months.

The latest statistical and coupled model forecasts show a large spread in
the forecasts for the next several months. While some indicate the
possibility that La Niņa
will develop during the second half of 2003, others indicate a resurgence of
El Niņo
conditions by the end of the year. However, based on current conditions and
recent observed trends, it appears likely that cold episode (La Niņa)
conditions will develop in the tropical Pacific during the next few months.

This discussion is a consolidated effort of NOAA and its
funded institutions. Weekly updates for SST, 850-hPa wind, OLR and features of the equatorial subsurface
temperature structure are available on the Climate Prediction Center web page at
http://www.cpc.ncep.noaa.gov (Weekly Update). Forecasts for the evolution of
El Niņo/La Niņa are updated monthly in CPC's Climate Diagnostics Bulletin Forecast Forum. To receive
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